A method of determining at least one drag torque acting on the input side of an automatic transmission, such that prior to the determination a separator clutch located between the transmission and an engine is disengaged. To be able to carry out the determination regardless of the type of transmission concerned, also prior to the determination, the transmission is shifted to neutral and subsequently the drag torque is calculated when the engine is deactivated. For this, a first gradient of a transmission input rotational speed is determined, before an engine rotational speed of the engine falls below the transmission input rotational speed, and a second gradient of the transmission input rotational speed is determined, after the engine rotational speed falls below the transmission input rotational speed. The method is stored as a computer program stored on data carrier of a drive-train control unit of a motor vehicle.